The Energy-Control and Path-Selection Method and Apparatus for Digital Diversity Signaling relates generally to the field of digital signal communications.
Digital communications systems frequently operate in fading channels, meaning that the amplitude and phase of a signal at the receiver are random variables. In a widely used analytic model for fading, the Rayleigh-fading channel with additive Gaussian noise, the likelihood of deep fading increases the error probability compared to non-fading channels. An increased error probability increases the likelihood that a transmitted “0” will be interpreted as a “1” by the receiver, or vice versa. Diversity signaling may be used to compensate for fading. Diversity signaling is the transmission of the same bit or set of bits to the same antenna multiple times, or transmission of the same bit or set of bits to multiple antennas. Diversity signaling can be performed by various means, including the use of several carrier frequencies, known as frequency diversity, or spatially separated antennas, called spatial diversity. Examples of other types of diversity include time, polarization, and path diversity.
Some methods for combining received diversity signals include maximal ratio combining, equal-weight combining, and selection diversity. Maximal ratio combining maximizes the mean signal-to-noise ratio (SNR) of the combined diversity transmissions in exactly the same fashion as a matched filter. Equal-weight combining involves processing received signals, such as by base-banding and filtering for the low-pass waveforms being sought, and summing the received diversity channels. Selection diversity uses a subset of all diversity channels, namely those with the largest SNRs, which are then combined with equal weights.
Conventional diversity systems typically do not transmit different energies on different diversity channels. For example, in some applications receivers or transmitters must be lightweight, battery powered, portable, and may need to operate in conjunction with several similar devices. These requirements limit the measurements, calculations, or adaptations the device or set of devices can perform to only the simplest types of diversity combining. Another reason diversity systems typically do not employ different energies on different diversity channels is that system designers often assume for simplicity that the noise and transmission loss are equal for each prospective diversity channel. Generally however, neither noise nor transmission loss are apt to be identical on all possible diversity channels. Therefore, it would be desirable to have a method for optimum energy-control in a diversity signaling system.